43 minutes ago, Stevey Y said:

Hi they did bugger about with the positioning of the sensors if you look through the archive I did post a diagram of where each sensor for the EGT system is, easiest way to check which one is wonky is to get the car up to running temp check the system on the diagnostics and systematically unplug each sensor one at a time and when the one that is reading low disappears just chase that plugs wiring back to that sensor, the plugs are all at the top of the engine on the bulkhead, the ULTRA system of EGT sensors is a pig therefore the one you might consider to be bank1 may be further downstream on my car the bank1 was on the group of three just after the cat if thats any help Euro five was a lot easier as they normally only had two or three sensors, its just a case of elimination all four sensors are the same part number so if you need to see how it works go to LLLcar parts and throw in your VIN and it comes up with a diagram showing where the sensors are but unfortunately it won't tell you which one is which, never any smoke with a failed EGT on Euro6 cars, it just won't regen.

Steve.

Thanks Steve. So I’ve located 2 and 3, uncoupled each of these to determine which was which. Where 3 and 4 are is anyone’s guess. I’ll take a look at you previous contributions for the layout of the sensors. 

38 minutes ago, NigelBywater said:

Thanks Steve. So I’ve located 2 and 3, uncoupled each of these to determine which was which. Where 3 and 4 are is anyone’s guess. I’ll take a look at you previous contributions for the layout of the sensors. 

Hi looking at the way yours runs the other two are one just after the EGR and another on the exhaust further down you can chase the wiring up from there the plugs will be different colours just to confuse the issue, just plumb in Big Townz in the C7 search history.

Steve.

11 minutes ago, Stevey Y said:

Hi looking at the way yours runs the other two are one just after the EGR and another on the exhaust further down you can chase the wiring up from there the plugs will be different colours just to confuse the issue, just plumb in Big Townz in the C7 search history.

Steve.

I think this is it.

On 3/3/2026 at 6:43 PM, Stevey Y said:

I think this is it.

Thanks for this. That said, I have no idea where  sensor 1 is under the bonnet based on this. As I said, 2 and 3 are easy to find but 1 is illusive when I look at the engine bay.  

4 hours ago, NigelBywater said:

Thanks for this. That said, I have no idea where  sensor 1 is under the bonnet based on this. As I said, 2 and 3 are easy to find but 1 is illusive when I look at the engine bay.  

Hi one is where you put three on your diagram, four is underneath on the exhaust unless you have the other software version which uses a box sensor to read both Nox/temp.

Steve.

21 minutes ago, Stevey Y said:

Hi one is where you put three on your diagram, four is underneath on the exhaust unless you have the other software version which uses a box sensor to read both Nox/temp.

Steve.

Did a little digging and found the official manual. Seems like 1 is underneath. 

21 hours ago, NigelBywater said:

Did a little digging and found the official manual. Seems like 1 is underneath. 

Hi did the diagnostic say it was sensor 1 that was reading low as if you look at the way they are described Bank 1 sensor 1 is just past sensor 2 thats the one I had to change, I am pretty certain that sensor three is the one further down just after the exhaust exits the DPF, some had a fourth about a couple of feet past that, if your fault was for sensor 1 change the one just beyond sensor 2 they are all the same sensor so if you buy one they all fit, as I said if you chase the wiring back to the plug and disconnect it while reading live data and the lower reading sensor goes blank that would be the offending sensor.

Steve.

21 hours ago, NigelBywater said:

Did a little digging and found the official manual. Seems like 1 is underneath. 

PS if you are going to do it yourself you will have to buy a serious set of sensor removal spanners as they will be very tight.

Steve.